Continued growth of urban load densities and the scarcity of available space for substation construction indicates a future market for metal-clad switchgear in voltage ratings above 15 KV. Circuit-breakers for use in this metal-clad switchgear range must fulfill a number of requirements, among which are reliability, long life, minimum maintenance, small size, quiet operation, and reasonable cost. The characteristics of sulfur-hexafluoride SF.sub.6 puffer-type interrupters make them well suited for this application. However, it is felt that for the best customer acceptance the interrupters preferably should be hermetically sealed.
Load-break disconnecting switches are quite old in the art, and in some instances employ an interrupting unit having separable interrupting arcing contacts in electrical series with the disconnecting switchblade to interrupt the incident arcing at the separable interrupting arcing contacts instead of at the disconnecting switch contacts. The prior art devices function to first effect initial opening of the interrupting assembly, and subsequently, effect opening of the serially related disconnecting switchblade without arcing thereat to completely isolate the circuit. U.S. Pat. No. 2,769,063, issued Oct. 30, 1956, to H. J. Lingal, is typical of such series-type devices. Other load-break disconnecting devices, which utilize a swinging movement of the free end of the disconnecting switchblade to effect the operation of the operating mechanism for the interrupting element, are set forth, for example, in U.S. Pat. No. 2,889,434, issued June 2, 1959, to H. J. Lingal, and assigned to the assignee of the instant application.
In some of the aforesaid load-break disconnecting switches, an insulating gas, such as sulfur-hexafluoride (SF.sub.6) gas, for example, is utilized for arc-extinguishing purposes. In still other devices, such as set forth in U.S. Pat. No. 2,737,556, issued Mar. 6, 1956, to MacNeill et al., a suitable arc-extinguishing liquid, such as oil, for example, may be utilized to advantage, although, as is well known, oil gives rise to the hazard of inflammability if the oil containers, or oil casing, should for some reason, fracture due to earthquake shock, vibration, gun shot, or from any other causes, and spill flammable oil into the surrounding switchyard area.
Modern circuit-breakers are efficient and reliable devices and perform their duties adequately. However, they are large and expensive; and in many cases, economies can be achieved with less-expensive devices. Such devices have been available for serveral years and range from load-interrupter switches, with interrupting ratings approximating their continuous current-carrying capabilities, to devices which can interrupt a few thousand amperes with modest transient-recovery voltage capabilities.
Over the past few years, development work performed with sulfur-hexafluoride (SF.sub.6) gas puffer-type circuit-interrupters has led to improvements in these puffer gas-type devices. Some of these improvements have been incorporated into the medium-fault-interrupting class devices, such as set forth in the instant patent application, thus expanding their field of application. Some of the advantages attained by the invention set forth herein include:
a. Simplicity of construction; PA1 b. 10,000 amperes interrupting capacity at 169 KV, for example, on a single contact break without using shunt capacitors or resistors; PA1 c. Transient-recovery capability on bus-faults corresponding to capability of circuit-breakers at maximum rating; PA1 d. Full insulation strength across the open contacts of the interrupter without requiring an open disconnecting switch; PA1 e. High-speed circuit-making and breaking in pressurized sulfur-hexafluoride SF.sub.6 gas which eliminates any arcing in air; and, PA1 f. Low noise level during switch operation.
Accordingly, it is desirable to improve upon the operating mechanisms of such load-break disconnecting switches or interrupter switches, per se, when used alone, and the present invention is particularly concerned with an improved motion-multiplying mechanism and having wide areas of application particularly for operating movable contacts in hermetically sealed casing structures.